Dynamic nuclear polarization of ~(29)Si nuclei in isotopically controlled phosphorus doped silicon

摘要

Dynamic nuclear polarization (DNP) of ~(29)Si nuclei in isotopically controlled silicon single crystals with the ~(29)Si isotope abundance f_(29Si) varied from 1.2% to 99.2% is reported. It was found that both the DNP enhancement and ~(29)Si nuclear spin-lattice relaxation time under saturation of the electron paramagnetic resonance transitions of phosphorus donors increase with the decrease in the ~(29)Si abundance. A remarkably large steady-state DNP enhancement, E~(ss)=2680 which is comparable to the theoretical upper limit of 3310, has been achieved through the "resolved" solid effect that has been identified clearly in the f_(29Si)=1.2% sample. The DNP enhancement depends not only on the ~(29)Si abundance but also on the electron spin-lattice relaxation time that can be controlled by temperature and/or illumination. The linewidth of ~(29)Si NMR spectra after DNP shows a linear dependence on f_(29Si) for f_(29Si)≤10% and changes to a square-root dependence for f_(29Si)≥50%. Comparison of experimentally determined nuclear polarization time with nuclear spin diffusion coefficients indicates that the rate of DNP is limited by the polarization transfer rather than by spin diffusion.